An optical transport network (OTN) transmission method specified in the International Telecommunication Union (TIU)-TG.709 standard is a method of transmitting client signals flowing into the optical network while storing the client signals in an optical channel transport unit (OTU). In addition to the payload storing the client signals, the OTU stores an overhead (OH) of an optical channel payload unit (OPU), an OH of an optical channel data unit (ODU), and an OH of the OTU.
In the OTN, a plurality of types of OTUs are defined capable of storing a plurality of types of client signals having different transmission rates as one signal. For example, client signals of up to about 1.25 Gbps are stored in an OTU0, and client signals of up to about 2.5 Gbps are stored in an OTU1. In addition, client signals of up to about 10 Gbps are stored in an OTU2, client signals of up to about 40 Gbps are stored in an OTU3, and client signals of up to about 100 Gbps are stored in an OTU4. Further, multiple types of ODUs are stored in the OTU.
As for the multiple types of ODUs, for example, client signals of up to about 1.25 Gbps are stored in an ODU0, and client signals of up to about 2.5 Gbps are stored in an ODU1. In addition, client signals of up to about 10 Gbps are stored in an ODU2, client signals of up to about 40 Gbps are stored in an ODU3, and client signals of up to about 100 Gbps are stored in an ODU4.
Lower-level ODUs are stored in the ODU. For example, the ODU0, ODU1, ODU2, and ODU3 are stored in the ODU4, and the ODU0, ODU1, and ODU2 are stored in the ODU3. Moreover, the ODU employs a multi-stage method capable of storing the lower-level ODUs to be nested in multiple stages. Further, the ODU which stores the lower-level ODUs is a higher order (HO)-ODU. The ODU which does not store the lower-level ODUs is a lower order (LO)-ODU. The ODU4 is obtained by, for example, multiplexing two HO-ODU2s, each storing eight LO-ODU0s, and two HO-ODU3s, each storing four LO-ODU2s.
Further, a separation unit of the transmission apparatus that conforms to the OTN separates the HO-ODU in a payload area of the received OTU and separates the data of the LO-ODU from the separated HO-ODU. Further, a multiplexing unit of the transmission apparatus stores the data of the LO-ODU in the HO-ODU, and outputs the stored HO-ODU while storing in the payload area of the OTU.
FIG. 14 is an explanatory diagram illustrating an example of a transmission system 100. The transmission system 100 illustrated in FIG. 14 includes client devices 101 of the OTU1, a network 102 of the OTU2, and a transmission apparatus 103. The transmission apparatus 103 is, for example, a transmission apparatus corresponding to OTU1×4 and OTU2×1.
The transmission apparatus 103 includes an OTU1 I/F 111, an ODU1 MUX/DMUX (Multiplexer/Demultiplexer) 112, a XC (Cross Connect) 113, an ODU processing unit 114, an ODU2 MUX/DMUX 115, and an OTU2 I/F 116. The OTU1 I/F 111 is a communication I/F between the transmission apparatus 103 and the client devices 101 of the OTU1. The OTU1 I/F 111 executes a calculation processing such as forward error correction (FEC) of the OTU1, and performs an error correction from the calculation results.
Further, the OTU1 I/F 111 detects the synchronization of an OTU OH of the OTU1. Further, the detection of the synchronization of the OH is performed by identification using a frame alignment signal (FAS) of the OTU OH of the OTU1. The OTU1 I/F 111 has an OH processing unit 111A which monitors the contents of the OTU OH while inserting the contents of the OTU OH into the OH area of the OTU1. The OH processing unit 111A has a register for each OTU1 I/F 111 to shift OTU1s to each other in order to ensure the synchronization between OTU1s of the OTU1 I/F 111. The number of OH processing units 111A is four in order to correspond to the OTU1 I/Fs 111.
The ODU1 MUX/DMUX 112 has a de-multiplex (DMUX) function of separating the data of the ODU0 which is the LO-ODU from the ODU1 which is the HO-ODU in the OTU1, and a multiplex (MUX) function of storing the data of the ODU0 in the ODU1. The XC 113 rearranges and outputs each data to a predetermined output destination on a LO-ODU basis. The ODU processing unit 114 has an OH processing unit 114A to monitor the contents of the ODU OH while inserting the ODU OH into an OH area of the ODU. The OH processing unit 114A has a register to shift data of the LO-ODUs to each other in order to ensure the synchronization between the data of the LO-ODUs on a LO-ODU basis. The number of the OH processing units 114A is eight in a total for each LO-ODU.
The ODU2 MUX/DMUX 115 has a DMUX function of separating the data of the ODU0 which is the LO-ODU from the ODU2 which is the HO-ODU, and a MUX function of storing the data of the ODU0 in the ODU2.
The OTU2 I/F 116 is a communication I/F between the transmission apparatus 103 and the network 102 of the OTU2. The OTU2 I/F 116 performs the FEC calculation processing of the OTU2, and inserts an FEC value into an FEC area of the OTU2. Further, the OTU2 I/F 116 detects the synchronization of an OTU OH of the OTU2. Further, the detection of the synchronization of the OTU OH is performed by identification using the FAS of the OTU OH of the OTU2. The OTU2 I/F 116 has an OH processing unit 116A which monitors the contents of the OTU OH while inserting the contents of the OTU OH into the OH area of the OTU2.
The OH processing unit 111A of the OTU1 I/F 111, upon receiving the OTU1 from the client device 101, checks the contents of the OTU OH of the OTU1, and then outputs the OTU1 to the ODU1 MUX/DMUX 112.
The ODU1 MUX/DMUX 112 separates the data of the ODU0 from the ODU1 in the OTU1, and outputs the separated data of the ODU0 to the XC 113. The XC 113 rearranges the data of the ODU0 from the ODU1 MUX/DMUX 112 to a predetermined output destination on a LO-ODU basis. Each OH processing unit 114A of the ODU processing unit 114 monitors the contents of the ODU OH of each ODU0. Further, each OH processing unit 114A, upon detecting a rewrite request of the ODU OH of each ODU0, rewrites a part or all of the contents of the ODU OH of each ODU0.
After the OH processing of the ODU OH of the ODU0, each OH processing unit 114A outputs the data of the ODU0 completed with the OH processing to the ODU2 MUX/DMUX 115. The ODU2 MUX/DMUX 115 stores the data of the ODU0 completed with the OH processing in the ODU2, stores the ODU2 in the payload area of the OTU2, and outputs the OTU2 to the OTU2 I/F 116.
The OH processing unit 116A of the OTU2 I/F 116 inserts the contents of the OTU OH into the OH area of the OTU2. Then, the OTU2 I/F 116 inserts the FEC value from the FEC calculation processing into the FEC area of the OTU2, and outputs the OTU2 to the network 102.
When transmitting the OTU1 of each client device 101 to the network 102 as the OTU2, the transmission apparatus 103 monitors the contents of the OTU OH of the OTU1, and then monitors and inserts the contents of the ODU OH for each LO-ODU in the OTU1. As a result, the transmission apparatus 103 stores the LO-ODU0 of each OTU1 from each client device 101 in the OTU2, and output the OTU2 to the network 102.
Upon receiving the OTU2 from the network 102 of the OTU2, the OTU2 I/F 116 identifies the FAS in the OTU OH of the OTU2 and detects the synchronization of the OTU2. Further, the OH processing unit 116A of the OTU2 I/F 116 monitors the contents of the OTU OH of the OTU2. The OTU2 I/F 116 separates the ODU2 from the payload area in the OTU2 and outputs the ODU2 to the ODU2 MUX/DMUX 115. The ODU2 MUX/DMUX 115 separates the data of the ODU0 from the ODU2 in the OTU2, and outputs the separated data of the ODU0 to the ODU processing unit 114.
Each OH processing unit 114A of the ODU processing unit 114 monitors the contents of the ODU OH of the ODU0 from the ODU2 MUX/DMUX 115 and, when rewriting the contents of the ODU OH, rewrites the contents of the ODU OH. The ODU processing unit 114 outputs the data of the OUD0 completed with the OH processing to the XC 113.
The XC 113 rearranges the data of each ODU0 from the ODU processing unit 114 to a predetermined output destination on a LO-ODU basis, and outputs the data of each ODU0 to the ODU1 MUX/DMUX 112. The ODU1 MUX/DMUX 112 stores the ODU0 from the XC 113 in the ODU1, stores the ODU1 in the payload area of the OTU1, and outputs the OTU1 to the OTU1 I/F 111. The OTU1 I/F 111 stores the ODU1 from the ODU1 MUX/DMUX 112 in the payload area of the OTU1, and inserts the contents of the OTU OH into the OH area of the OTU1. Further, the OTU1 I/F 111 FEC calculates the OTU1, and inserts the FEC value into the FEC area in the OTU1. Then, the OTU1 I/F 111 outputs the OTU1 to the client device 101.
When transmitting the OTU2 from the network 102 to each client device 101, the transmission apparatus 103 monitors the OTU OH of the OTU2, and then monitors and inserts the contents of the ODU OH for each LO-ODU in the OTU2. As a result, the transmission apparatus 103 separates the OTU2 from the network 102 into the OTU1, and outputs the OTU1 to each client device 101.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2011-146917.